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The US Environmental Protection Agency (USEPA) considers sediment toxicity tests as conditional registration requirements for pesticides with soil Kd ≥50 L/kg‐solid, Koc ≥1000 L/kg‐organic carbon, or log Kow ≥3. The hydrophobicity of these compounds often necessitates use of solvents to ensure accurate and homogeneous dosing of spiked‐sediment studies. For sediment tests, a volatile solvent (e.g., acetone) is generally used as a transient carrier. Due to low water solubility, test material is dissolved in a volatile solvent to create stock solutions. A measured aliquot of stock solution is then mixed with sand substrate, after which the solvent is evaporated. This spiking process results in negligible solvent exposure to organisms. In 2016, USEPA released final ecotoxicity test guidelines for subchronic freshwater (850.1735) and marine (850.1740) sediment test. These methods provide an option for conducting experiments with only a solvent control and no negative control. To adopt this testing strategy, functional equivalency between the negative and solvent control must be demonstrated. These test guidelines describe specific factors that should be considered for evaluating functional equivalency, including (a) the concentration of solvent in the test sediment after evaporation, (b) the levels of solvent that are known to affect organism health, (c) the known impurities in the solvent and their potential impact on organism health, and (d) the historical organism performance of solvent versus negative controls. Our analysis considers these factors and overall supports the elimination of the negative control requirement because this change is unlikely to impact the robustness or interpretability of spiked‐sediment toxicity tests. Environ Toxicol Chem 2024;43:1740–1746. © 2023 CropLife America. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC. [ABSTRACT FROM AUTHOR]

Fishes have spread into previously fishless wetlands, likely affecting other species. In the Prairie Pothole Region of North America, the invasion of fish into wetlands is facilitated by interactions of altered land use, climate, and hydrology. We aimed to understand the effects of fishes on amphipods, which are macroinvertebrates that vertebrates rely on as forage. We hypothesized the presence and abundance of fish, particularly benthivores, would have detrimental effects on amphipod abundance. Our study design targeted a large gradient of amphipod abundances among wetlands, including very high abundances of two amphipod species: Gammarus lacustris and Hyalella azteca. We found that fishless basins had twice as many amphipods as those with fish, on average. Gammarus lacustris were not detected in the presence of Black Bullhead Ameiurus melas. The abundance of both amphipod species had negative associations with the most common fishes, Fathead Minnow Pimephales promelas and Brook Stickleback Culaea inconstans. A multivariate community analysis showed the benthivore-fish functional feeding guild was negatively associated with the amphipod community, as hypothesized. However, our study design captured several wetlands with anomalies of high abundances of both fish and amphipods, obscuring their relationships. Our results aid resource managers by confirming several fish guilds and species are associated with lower abundances of amphipods. These findings can inform resource managers who make decisions about managing for fish and wildlife; for example, they may choose to manage existing fish populations or protect existing wetlands with high amphipod densities from new fish invasions. [ABSTRACT FROM AUTHOR]

Contamination by polycyclic aromatic hydrocarbons (PAH) in freshwater ecosystems represents a serious environmental problem. When they enter the water, either by oil spills or industrial discharges, they adhere to suspended particles, accumulating in sediments and causing them to be absorbed by aquatic organisms, such as decapods and amphipods. Therefore, to evaluate the effects of PAHs on Macrobrachium borelli and Hyalella azteca, a bibliographic compilation was made considering the axes of hydrocarbon toxicity and adaptation mechanisms for these pollutants. The results for decapods indicate a high toxicity for the water-soluble fraction with diesel, although this does not prevent normal hatching of eggs. For amphipods, it was found that, according to their mortality, it is a more sensitive species than other organisms, such as chironomids. In addition, the sublethal effects due to PAH exposure vary in the affectation in the size and behavior of the organism, as well as DNA damage. Finally, the adaptive mechanisms it possesses are not considered effective for the survival of the species. [ABSTRACT FROM AUTHOR]

Bioconcentration tests using the freshwater amphipod Hyalella azteca as an alternative to conventional fish tests have recently received much attention. An appropriate computational model of H. azteca could help in understanding the mechanisms behind bioconcentration, in comparison to the fish as test organism. We here present the first mechanistic model for H. azteca that considers the single diffusive processes in the gills and gut. The model matches with the experimental data from the literature quite well when appropriate physiological information is used. The implementation of facilitated transport was essential for modeling. Application of the model for superhydrophobic compounds revealed binding to organic matter and the resulting decrease in bioavailable fraction as the main reason for the observed counterintuitive decrease in uptake rate constants with increasing octanol/water partition coefficient. Furthermore, estimations of the time needed to reach steady state indicated that durations of more than a month could be needed for compounds with a log Kow > 8, limiting the experimental applicability of the test. In those cases, model-based bioconcentration predictions could be a preferable approach, which could be combined with in vitro biotransformation measurements. However, our sensitivity analysis showed that the uncertainty in determining the octanol/water partition coefficients is a strong source of error for superhydrophobic compounds. [ABSTRACT FROM AUTHOR]

The acceleration of global climate change draws increasing attention towards interactive effects of temperature and organic contaminants. Many studies reported a higher sensitivity of aquatic invertebrates towards contaminant exposure with increasing or fluctuating temperatures. The hypothesis of this study was that the higher sensitivity of invertebrates is associated with the changes of toxicokinetic processes that determine internal concentrations of contaminants and consequently toxic effects. Therefore, the influence of temperature on toxicokinetic processes and the underlying mechanisms were studied in two key amphipod species (Gammarus pulex and Hyalella azteca). Bioconcentration experiments were carried out at four different temperatures with a mixture of 12 exposure relevant polar organic contaminants. Tissue and medium samples were taken in regular intervals and analysed by online solid‐phase extraction liquid chromatography high‐resolution tandem mass spectrometry. Subsequently, toxicokinetic rates were modelled and analysed in dependence of the exposure temperature using the Arrhenius equation. An exponential relationship between toxicokinetic rates versus temperature was observed and could be well depicted by applying the Arrhenius equation. Due to a similar Arrhenius temperature of uptake and elimination rates, the bioconcentration factors of the contaminants were generally constant across the temperature range. Furthermore, the Arrhenius temperature of the toxicokinetic rates and respiration was mostly similar. However, in some cases (citalopram, cyprodinil), the bioconcentration factor appeared to be temperature dependent, which could potentially be explained by the influence of temperature on active uptake mechanisms or biotransformation. The observed temperature effects on toxicokinetics may be particularly relevant in non‐equilibrated systems, such as exposure peaks in summer as exemplified by the exposure modelling of a field measured pesticide peak where the internal concentrations increased by up to fourfold along the temperature gradient. The results provide novel insights into the mechanisms of chemical uptake, biotransformation and elimination in different climate scenarios and can improve environmental risk assessment. [ABSTRACT FROM AUTHOR]

Freshwater organisms are often exposed to contaminants such as heavy metals from stormwater discharges, which are dependent on rainfall duration and intensity. Therefore, standardized (48‐ or 96‐h) continuous exposure methods developed for whole effluent toxicity (WET) testing might not always accurately convey the effects of stormwater and runoff contaminants. The present study characterized the acute toxicity of copper (Cu), zinc (Zn), and cadmium (Cd) to freshwater amphipods (Hyalella azteca) and cadmium (Cd) to water fleas (Ceriodaphnia dubia) using a modified exposure design that integrated relevant pulsed durations and included post‐exposure monitoring. Less than 24‐h‐old C. dubia and 7 to 8‐day‐old H. azteca were exposed to water spiked with Cu, Zn, or Cd using 6‐, 12‐, 26‐, or 96‐h durations under standard laboratory conditions and monitored for cumulative mortality and reproduction (C. dubia only). Lethal effect (LC10s, LC25s, LC50s) and reproductive effect (EC25s, EC50s) were determined based on either mortality or reproduction of organisms at the end of each pulse (6, 12, or 26 h) and at the end of their respective tests (96 h). For all metals exposed to each organism, acute toxicity was found to be highest for the (96 h) continuous exposures. For pulsed exposures, mortality continued to increase following transfer to clean water for post‐exposure monitoring. These results indicate a latent effect of Cu, Zn, and Cd to H. azteca and Cd to C. dubia. The present study concluded that using the continuous (48‐ or 96‐h) WET exposure method overestimates the effects of stormwater and runoff contaminants. However, pulsed exposures without post‐exposure monitoring also underestimate the toxicity of contaminants. The proposed pulsed exposure design provides a compromise that is more realistic than current WET methods to assess impacts from episodic events and accounts for potential latent effects that may be overlooked without monitoring post‐exposure. Environ Toxicol Chem 2022;41:2488–2499. © 2022 SETAC [ABSTRACT FROM AUTHOR]

On August 4, 2014, a tailings dam failed at the Mount Polley copper and gold mine near Likely, British Columbia, Canada, releasing approximately 25 M m 3 of contaminated water and solid tailings material into Polley and Quesnel lakes. Water, sediment, freshwater scuds (Hyalella azteca), and mayfly larvae (Ephemeroptera) were collected during the summer of 2018 from Polley Lake, affected and unaffected sites in Quesnel Lake, and both mine-contaminated and clean far-field sites as references. Analytical results indicated that invertebrates from sites affected by the tailings breach had elevated metal concentrations relative to those from non-affected or reference sites. We conducted a controlled laboratory exposure to determine if laboratory-reared Hyalella azteca metal concentrations were related to field-collected water or sediments from the same sites as the field study. Half of the replicates prevented amphipods from directly contacting sediments (water-only exposure), while the other half allowed them direct access (sediment and water exposure). Whole-body Cu concentration was highest in Hyalella exposed to substrate from the most contaminated sites as well as in treatments where they were allowed direct access to sediments. Hyalella having direct access to metal-contaminated sediments showed reduced survival and growth relative to those in reference or control treatments. These results suggest that metals from the fine sediments associated with the Mount Polley mine disaster are bioavailable and potentially toxic to epibenthic invertebrates, even several years after the initial breach. [ABSTRACT FROM AUTHOR]

Perfluorooctane sulfonic acid (PFOS) is a ubiquitous and persistent contaminant in aquatic ecosystems. Chronic toxicity information for aquatic organisms is limited, therefore we conducted chronic PFOS toxicity tests for four model organisms commonly used for freshwater toxicology assays: Chironomus dilutus (midge), Ceriodaphnia dubia (water flea), Hyalella azteca (amphipod) and Danio rerio (zebrafish). The 16-day survival test with C. dilutus resulted in the lowest PFOS exposure concentrations to cause significant impacts, with reduced survival at 1 µg/L, a LC50 of 7.5 µg/L, and a growth EC10 of 1.5 µg/L. D. rerio was the next most sensitive species, with a 30-day LC50 of 490 µg/L and reduced growth at 260 µg/L. Effects for C. dubia and H. azteca occurred at concentrations a thousand-fold higher than for C. dilutus. H. azteca had a 42-day LC50 of 15 mg/L, an EC50 of 3.8 mg/L for reproduction (neonates per female) and an EC50 of 4.7 mg/L for growth. C. dubia was similarly tolerant of PFOS, with a 6-day LC50 of 20 mg/L for survival and an EC50 of 7 mg/L for reproduction (neonates per adult). H. azteca, C. dubia, and, to a lesser extent, D. rerio, appear tolerant of PFOS concentrations typically found in the environment. However, in agreement with previous studies, C. dilutus was particularly sensitive to PFOS exposure, with lethal and sublethal effects occurring at concentration levels present at highly contaminated sites.

Purpose: Sequential extraction procedure (SEP) verifies which of the bioavailable extraction phases has the greatest potential for releasing metals from a given set of samples. The hypothesis here is that it is possible to find a correlation between the presence of metals in different bioavailable chemical fractions (data obtained by SEP) and results of ecotoxicological tests conducted with Hyalella azteca, under controlled laboratory conditions in field-collected sediment samples. Methods: Sediment samples from an urban lake were submitted to SEP to analyze the fractionation of heavy metals (Cd, Cr, Cu, Ni, Pb and Zn) in bioavailable and non-bioavailable extraction phases. Spearman correlation, Mann–Whitney U test, hierarchical cluster analysis (HCA), and principal component analysis (PCA) assessed the influence of heavy metals on the survival of the test organism. Results and discussions: Copper and Cr, mainly bound to the oxidizable phase, were the metals that were most closely related to the mortality of H. azteca (PC1). Zinc bound to the oxidizable phase and Pb also showed an association with the mortality of the test organism, but with less representation (PC2). Cadmium and Ni were the metals less correlated with the low survival of H. azteca. Conclusion: The results indicate that the bioavailable chemical fractions may reflect the interactive effect of metals in mixtures on the survival of the test organism. [ABSTRACT FROM AUTHOR]

Abstract Organophosphate (OP) and carbamate (CM) insecticides are widely used in the United States and share the same mode of toxic action. Both classes are frequently documented in aquatic ecosystems, sometimes at levels that exceed aquatic life benchmarks. We previously identified a population of the nontarget amphipod, Hyalella azteca, thriving in an agricultural creek with high sediment levels of the OP chlorpyrifos, suggesting the population may have acquired genetic resistance to the pesticide. In the present study, we surveyed 17 populations of H. azteca in California to screen for phenotypic resistance to chlorpyrifos as well as genetic signatures of resistance in the acetylcholinesterase (ace‐1) gene. We found no phenotypic chlorpyrifos resistance in populations from areas with little or no pesticide use. However, there was ~3‐ to 1,000‐fold resistance in H. azteca populations from agricultural and/or urban areas, with resistance levels in agriculture being far higher than urban areas due to greater ongoing use of OP and CM pesticides. In every case of resistance in H. azteca, we identified a glycine‐to‐serine amino acid substitution (G119S) that has been shown to confer OP and CM resistance in mosquitoes and has been associated with resistance in other insects. We found that the G119S mutation was always present in a heterozygous state. Further, we provide tentative evidence of an ace‐1 gene duplication in H. azteca that may play a role in chlorpyrifos resistance in some populations. The detection of a genetically based, adaptive OP and CM resistance in some of the same populations of H. azteca previously shown to harbor a genetically based adaptive pyrethroid resistance indicates that these nontarget amphipod populations have become resistant to many of the insecticides now in common use. The terrestrial application of pesticides has provided strong selective pressures to drive evolution in a nontarget, aquatic species.

Wild-type Hyalella azteca are highly sensitive to pyrethroid insecticides and typically do not survive exposure; however, pyrethroid bioaccumulation by insecticide-resistant H. azteca is an important potential risk factor for the transfer of pyrethroids to higher trophic species in aquatic systems. In the current study, four populations of pyrethroid-resistant H. azteca with corresponding sediment samples were sampled throughout the year, and nine-current use pyrethroids (tefluthrin, fenpropathrin, bifenthrin, cyhalothrin, permethrin, cyfluthrin, cypermethrin, esfenvalerate and deltamethrin) were measured. Bifenthrin was detected in every pyrethroid-resistant H. azteca tissue sample, up to 813 ng/g lipid, while cyhalothrin and permethrin were detected in fewer (18 and 28%, respectively) samples. Concurrent sampling of the sediment showed total pyrethroid concentrations exceeding toxic unit thresholds for non-resistant H. azteca survival, and confirmed the ubiquitous presence of bifenthrin at each site and sampling event. Bifenthrin concentrations in H. azteca tended to be higher in samples collected in winter months, and seasonal factors, such as temperature and rainfall, may have contributed to the noted differences in bioaccumulation. Finally, the bifenthrin and permethrin biota-sediment accumulation factors (BSAF) for pyrethroid-resistant H. azteca were similar to the BSAF values for less sensitive invertebrates, and therefore the development of resistance may enable an additional pathway for trophic transfer of pyrethroids in species that would otherwise be too sensitive to survive the exposure. [ABSTRACT FROM AUTHOR]

Background: Manufactured nanomaterials (MNMs) are released into the environment in increasing quantities. Consequently, MNMs also reach the aquatic environment, where they can interact with different organisms. Previous studies have already shown that filter-feeding bivalves can ingest nanomaterials from the surrounding water leading to higher concentration of the material. Furthermore, they have been shown to be vectors for environmental chemicals and pathogens to other organisms, as their feces/pseudofeces (F/pF) play a crucial role as a food source for other species. We exposed bivalves (Corbicula sp.) to MNMs and performed experiments to investigate the possible transport of MNMs by their feces to the benthic amphipod Hyalella azteca. Silver (Ag) and gold (Au) nanoparticles (NPs) as well as fluorescent polystyrene nanoparticles were used in this study. They allowed the investigation of the metal content of the bivalves' feces and the amphipods feeding on it, as well as the localization of the fluorescent particles in the body of the animals. Results: Examination of the feces by fluorescence microscope and determination of the total metal content by inductively coupled plasma mass spectrometry (ICP-MS) showed a high accumulation of the exposed MNMs in the F/pF. The examination of fecal matter, using transmission electron microscopy confirmed the nanoparticulate character of the metals in the examined fecal matter. After exposure of amphipods to the MNMs containing fecal matter, the fluorescent MNMs were localized in the animals gut. The chronic exposure of juvenile amphipods over 21 days to feces enriched with Au MNMs caused significant effects on the growth of the amphipods. The transfer of both metals (Ag and Au) from the fecal matter to the amphipods was confirmed after total metal measurements. Conclusion: Probably, for the first time, it has been shown that when exposed to MNMs bivalves can transfer these particles to other benthic species. Transfer is via released F/pF upon which the benthic species feed and thus could ingest the particles. The high concentrations of MNMs in the fecal matter raises concerns about the potential accumulation and transfer of the materials and associated ecotoxicological effects in invertebrates such as benthic amphipods. [ABSTRACT FROM AUTHOR]

The frequency of wildfire is expected to increase with time as a function of climate change. Recent studies in our laboratory have demonstrated that pyrogenic polycyclic aromatic hydrocarbons can cause greater‐than‐additive effects in Hyalella azteca in the presence of low concentrations of Cu. We hypothesized that freshwater animals inhabiting Cu‐contaminated sites, such as those in the vicinity of Cu mines, may be vulnerable to nonadditive toxicity from contaminants released by wildfires. To investigate the interaction between Cu and water conditioned by burnt wood ash (fire extract), we exposed H. azteca for 14 d to binary mixtures of 225 mg/kg Cu‐enriched artificial sediment (225 mg Cu/kg) and a fire extract dilution series (12.5, 25, 50, 75, and 100%). All binary mixtures of Cu‐enriched sediment and fire extract resulted in complete mortality with the exception of Cu‐enriched sediment + 12.5% fire extract. The combination of Cu‐enriched sediment with 12.5% fire extract had a more‐than‐additive effect on survival and tissue Cu concentration, but there was no reduction in growth or acetylcholinesterase activity compared to the 225 mg/kg Cu–contaminated sediment or fire extract control, respectively. Acetylcholinesterase activity was significantly reduced in amphipods exposed to fire extract, but the presence of Cu did not exacerbate this effect. The results suggest that Cu‐contaminated water bodies that receive runoff from wildfires are at risk of enhanced toxicity. Environ Toxicol Chem 2020;39:1988–1997. © 2020 SETAC [ABSTRACT FROM AUTHOR]

Bioaccumulation assessment predominantly relies on the bioconcentration factor (BCF) as the sole decisive metric. The test guideline 305 by the Organisation for Economic Co‐operation and Development (OECD) provides the standard procedure for deriving this in vivo fish BCF, which is not only expensive and labor‐intensive, but also requires many animals. Accordingly, there is a great need for and interest in alternative methods that can help to reduce, replace, and refine vertebrate tests, as described in the 3R principles. Two alternative approaches have been developed: the bioconcentration test with the freshwater amphipod Hyalella azteca and the OECD test guideline 319 which provides a method to determine experimentally derived in vitro metabolism rates that can then be incorporated into in silico prediction models for rainbow trout BCF calculation. In the present study both alternative methods were applied to 5 substances of different physicochemical characteristics. The results were compared with literature values of fish in vivo BCFs and additional BCFs obtained with the alternative methods, if available. Potential differences between the results of the test methods are discussed utilizing information such as in vivo metabolism rates. The currently available data set suggests that these 2 alternative methods pose promising alternatives to predict bioaccumulation in fish, although defined applicability domains have yet to be determined. Environ Toxicol Chem 2020;39:1813–1825. © 2020 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC [ABSTRACT FROM AUTHOR]

Traditionally, due to different hardware requirements, nuclear magnetic resonance (NMR) has developed as two separate fields: one dealing with solids, and one with solutions. Comprehensive multiphase (CMP) NMR combines all electronics and hardware (magic angle spinning [MAS], gradients, high power Radio Frequency (RF) handling, lock, susceptibility matching) into a universal probe that permits a comprehensive study of all phases (i.e., liquid, gel‐like, semisolid, and solid), in intact samples. When applied in vivo, it provides unique insight into the wide array of bonds in a living system from the most mobile liquids (blood, fluids) through gels (muscle, tissues) to the most rigid (exoskeleton, shell). In this tutorial, the practical aspects of in vivo CMP NMR are discussed including: handling the organisms, rotor preparation, sample spinning, water suppression, editing experiments, and finishes with a brief look at the potential of other heteronuclei (2H, 15N, 19F, 31P) for in vivo research. The tutorial is aimed as a general resource for researchers interested in developing and applying MAS‐based approaches to living organisms. Although the focus here is CMP NMR, many of the approaches can be adapted (or directly applied) using conventional high‐resolution magic angle spinning, and in some cases, even standard solid‐state NMR probes. [ABSTRACT FROM AUTHOR]

Organophosphate (OP) and carbamate (CM) insecticides are widely used in the United States and share the same mode of toxic action. Both classes are frequently documented in aquatic ecosystems, sometimes at levels that exceed aquatic life benchmarks. We previously identified a population of the nontarget amphipod, Hyalella azteca, thriving in an agricultural creek with high sediment levels of the OP chlorpyrifos, suggesting the population may have acquired genetic resistance to the pesticide. In the present study, we surveyed 17 populations of H. azteca in California to screen for phenotypic resistance to chlorpyrifos as well as genetic signatures of resistance in the acetylcholinesterase (ace‐1) gene. We found no phenotypic chlorpyrifos resistance in populations from areas with little or no pesticide use. However, there was ~3‐ to 1,000‐fold resistance in H. azteca populations from agricultural and/or urban areas, with resistance levels in agriculture being far higher than urban areas due to greater ongoing use of OP and CM pesticides. In every case of resistance in H. azteca, we identified a glycine‐to‐serine amino acid substitution (G119S) that has been shown to confer OP and CM resistance in mosquitoes and has been associated with resistance in other insects. We found that the G119S mutation was always present in a heterozygous state. Further, we provide tentative evidence of an ace‐1 gene duplication in H. azteca that may play a role in chlorpyrifos resistance in some populations. The detection of a genetically based, adaptive OP and CM resistance in some of the same populations of H. azteca previously shown to harbor a genetically based adaptive pyrethroid resistance indicates that these nontarget amphipod populations have become resistant to many of the insecticides now in common use. The terrestrial application of pesticides has provided strong selective pressures to drive evolution in a nontarget, aquatic species. [ABSTRACT FROM AUTHOR]

Ecological effects of gold nano-particles (AuNP) are examined due to growing use in consumer and industrial materials. This study investigated uptake and movement of AuNPs through an aquatic food chain. Simple (single-species) and diverse (multi-species) periphyton communities were exposed to AuNP (0, 100, 500 µg L−1 treatments). AuNP quickly aggregated and precipitated from the water column, suggesting it is an insignificant route of AuNP exposure even at elevated concentrations. Gold was measured in 100 and 500 µg L−1 periphyton treatments. Gold accumulation was similar between periphyton treatments, suggesting physical processes were important for AuNP basal accumulation. Hyalella azteca and Lymnea stagnalis whole body tissue analysis indicated gold accumulation may be attributed to different feeding mechanisms, general versus selective grazing, respectively. Results suggest trophic transfer of AuNP is organism specific and aggregation properties of AuNP are important when considering fate of nano-particles in the environment and movement through aquatic food webs. [ABSTRACT FROM AUTHOR]

Polycyclic aromatic hydrocarbons are organic chemicals consisting of a small number of benzene rings. PAHs are exposed to the environment by events such as Crude oil spills, even though they are substances present in the environment. Exposure of PAHs to the environment will affect not only the environment, but also the living organisms and the ecosystem as a whole. The effects of PAHs vary widely depending on the type of PAHs and have been studied for a long time. However, there are only 16 kinds of PAHs defined by US EPA, and there are more kinds of PAHs present in the environment. Therefore, it is time- and space-limited to judge the toxicity of all kinds of PAHs by evaluating them. In all cases, the tendency of research is shifting toward predicting toxicity evaluation through modeling rather than the direction of toxicity evaluation. In this study, we constructed a quantitative structure-activity relationship (QSAR) model, one of the molecular structure activation models, and predicted the correlation between the toxicity value and the logKow value of PAHs. Basically, as the logKow value increases, the median effective concentration (EC50) tends to decrease. Compared with the previous studies, Hyalella azteca showed this tendency, but Daphnia magna showed different results when exposed to Naphthalene. The RMSE(Root Mean Square Error) values of Daphnia magna and Hyalella azteca were 6.0049 and 5.9980, respectively, when the QSAR model was constructed using the toxicity data for PAHs. We confirmed the validity of the QSAR model in this study by comparing the results of exposing Daphnia magna to PAHs and the ECOSAR data, one of the existing models. The R2 value was found to be 0.9356. This study suggests that it may be helpful to predict the toxicity evaluation and to prepare countermeasures for accidents such as Crude oil spill. It is thought that if more data base is created by using additional types of PAHs and species in the same way as this study in the future, it will help to construct the modeling. [ABSTRACT FROM AUTHOR]

The objective of the present study was to establish a culture of Hyalella azteca that could be used for laboratory toxicity testing in low–ionic strength waters with electrical conductivities of <200 μS/cm. A wild strain of H. azteca was collected from Twin Lake, a small seepage lake with an electrical conductivity of 81 ± 27 μS/cm located on the property of Chalk River Laboratories in Chalk River, Canada. To determine the minimum aqueous ion requirements for an optimal culturing medium for the Twin Lake strain, Twin Lake was monitored for water quality and ionic content over 4 yr. Water quality parameters were averaged and used to formulate a medium containing NaHCO3, CaCl2, MgSO4, KCl, NaBr, NaF, and LiCl, with an electrical conductivity of 89 ± 3 μS/cm. By evaluating survival and reproduction, it was concluded that this artificial medium promoted survival and supported reproduction (10 ± 4 neonates/female/wk) of the Twin Lake amphipod. The Twin Lake strain of H. azteca can, therefore, be maintained in laboratory settings, and this allows for toxicity testing to be conducted on low–ionic strength waters. Environ Toxicol Chem 2019;38:585–590. © 2019 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals, Inc. on behalf of SETAC. [ABSTRACT FROM AUTHOR]

The leaf-shredding crustacean Hyalella azteca, which is indigenous to Northern and Central America, is used to assess environmental risks associated with (metal-)contaminated sediments and to propose sediment quality standards also in Europe. Yet, it is unknown if H. azteca is protective for European crustacean shredders. We thus compared the sensitivity of H. azteca with that of the European species Asellus aquaticus and Gammarus fossarum towards copper- and cadmium-contaminated sediments (prepared according to OECD 218) under laboratory conditions employing mortality and leaf consumption as endpoints. H. azteca either reacted approximately fourfold more sensitive than the most tolerant tested species (as for cadmium) or its sensitivity was only 1.6 times lower than the highest sensitivity determined (as for copper), which should be covered by safety factors applied during risk assessments. Therefore, the results for the sediment type and the two heavy metals tested during the present study in combination with the existence of standardized testing protocols, their ease of culture, and short generation time, suggest H. azteca as suitable crustacean model shredder for assessing the toxicity of sediment-associated metals in Europe. [ABSTRACT FROM AUTHOR]

Bioconcentration factors (BCF) for regulatory purposes are usually determined by fish flow-through tests according to technical guidance document OECD 305. Fish bioconcentration studies are time consuming, expensive, and use many laboratory animals. The aim of this study was to investigate whether the freshwater amphipod Hyalella azteca can be used as an alternative test organism for bioconcentration studies. Fourteen substances of different hydrophobicity (log Kow 2.4-7.6) were tested under flow-through conditions to determine steady state and kinetic bioconcentration factors (BCFss and BCFk). The results were compared with fish BCF estimates for the same substances described in the literature to show the relationship between both values. Bioconcentration studies with the freshwater amphipod H. azteca resulted in BCF estimates which show a strong correlation with fish BCF values (r2 = 0.69). Hyalella BCF values can be assessed in accordance with the regulatory B criterion (BCF > 2000, i.e., REACH) and thereby enable the prediction of B or non-B classification in the standard fish test. Therefore, H. azteca has a high potential to be used as alternative test organism to fish for bioconcentration studies. [ABSTRACT FROM AUTHOR]

Abstract Negative effects of environmental antibiotics on non-target organisms were observed in studies at various levels of the biological organization. Yet, studies combining the effects at multiple levels were required to interpret their ecological frequencies in a broader context. Currently, effects of sulfamethoxazole (SMX) was studied on the amphipod Hyalella azteca which is important in ecological stability. At the biochemical level, effects on the antioxidant capacities showed stimulation with an inverse U-shaped change over the concentrations. The stimulation was greater in male than in females. Effects on the oxidative stress showed a U-shaped change which included stimulation and inhibition in males, and solely stimulation in females. The stimulation was less in males than in females. Effects on acetylcholinesterase (AChE) activities in both sexes were well correlated with those on oxidative stress (p < 0.05). At the individual level, effects on the body weight showed an inverse U-shaped change over concentrations, and the stimulation was greater in males than in females. The stimulations were significantly correlated with the male oxidative stress (p < 0.01), and male (p < 0.1) and female AChE activities (p < 0.05). Effects of SMX on the pre-copulation behavior also showed an inverse U-shaped change which correlated with male and female antioxidant capacities (p < 0.05) and the male body weight (p < 0.05). At the population level, effects on the reproduction showed an inverse U-shaped change over concentrations, and they significantly correlated with the male body weight (p < 0.05) and the pre-copulation behavior (p < 0.05). Summing up, SMX provoked simultaneous disturbances on the amphipod at multiple levels with sex-dependent responses. Graphical abstract Image 1 Highlights • Effects of sulfamethoxazole was studied on the amphipod Hyalella azteca. • Disturbances on pre-/anti-oxidant status were greater in males than in females. • AChE activity changes, greater in males, were correlated with oxidative stress. • Stimulation and inhibition on male growth were greater than those on females. • Stimulation on reproduction were well correlated with pre-copulation behavior. Sulfamethoxazole caused sex-dependent effects on pro-/anti-oxidant status, AChE activities, and growth, and stimulated behavior and reproduction in Hyalella azteca. [ABSTRACT FROM AUTHOR]

Non-target organisms in aquatic environments may experience lethal or sublethal effects following exposure to contaminants. Most protocols and regulations, however, are designed to provide protection from lethal effects and are thus based on conventional estimates of population lethality. The relative lack of reliable behavioral endpoints makes it challenging to implement regulations that are similarly protective against sublethal toxicity. The objective of this study was to quantify the avoidance behavior of Hyalella azteca when exposed to three insecticides—bifenthrin (B), chlorpyrifos (C), and permethrin (P)—at a range of estimated lethal concentrations. A two-choice behavioral arena was used for each chemical to quantify H. azteca activity and time spent in either uncontaminated sediment or sediment spiked at concentrations reflecting estimated 48-h lethal concentrations (LC 50 , LC 25 , and LC 10). For all three insecticides, naïve H. azteca demonstrated a preference for the uncontaminated sediment over the contaminated sediment at the LC 50 (B: 312 ng/g OC ; C: 1265 ng/g OC ; P: 5042 ng/g OC) and LC 25 (B: 230 ng/g OC ; C: 859 ng/g OC ; P: 3817 ng/g OC), spending significantly more time in the uncontaminated side of the arena. H. azteca did not avoid sediment at LC 10 (B: 204 ng/g OC ; C: 609 ng/g OC ; P: 1515 ng/g OC) levels, indicating the existence of a potential threshold of detection. Despite the lack of substrate preference at this exposure level, H. azteca were nevertheless more active (i.e., increased zone-switching) when exposed to bifenthrin at the LC 10 , suggesting a possible irritation response (e.g., movement after exposure) to this chemical. Our results provide evidence that H. azteca exhibit innate avoidance responses to sediments contaminated with common insecticides at concentrations below those represented by traditional toxicological endpoints (e.g., LC 50). The sensitivity and ease with which this behavioral endpoint can be assayed demonstrates the potential utility of behavioral endpoints in toxicological assessments using model organisms. [Display omitted] • Avoidance behavior is a sensitive endpoint with population-level consequences. • Hyalella azteca avoided insecticides in sediment at and below the LC 50 and LC 25. • Avoidance was not detected at insecticide concentrations equal to the LC 10. • Increased activity at the bifenthrin LC 10 suggest a threshold of detection. • We advocate for the utility of avoidance as an informative behavioral endpoint. [ABSTRACT FROM AUTHOR]

The degradation of benthic communities (benthos) is one of four remaining beneficial use impairments (BUIs) in the Eighteenmile Creek Area of Concern (AOC), located on the south shore of Lake Ontario in New York. The historical rationale for listing this BUI as impaired relied heavily on inferred or expected impact to benthic communities based on elevated contaminant concentrations in bed sediments from past industrial and municipal discharges, hazardous-waste disposal, and pesticide usage. Previous assessments of macroinvertebrate community condition in the AOC have produced inconclusive results, and it remains unclear if contaminated sediments are impairing benthic communities. In 2021, a comprehensive assessment of macroinvertebrate community condition and sediment toxicity was conducted at eight sites in the AOC and six sites in a reference area on Oak Orchard Creek to determine if the removal criteria for this BUI have been met or if additional remedial measures are needed. The New York multi-metric index of biological integrity classified the mean community condition across AOC sites as slightly impacted, and 10-day toxicity tests with Chironomus dilutus and Hyalella azteca found no evidence of toxicity in AOC sediments. Equivalence testing indicated that community condition, and survival and growth of both test species, were not inferior in the AOC relative to the reference area. The weight of evidence from this study and other relevant datasets indicate that sediment contamination is not causing measurable impairment to benthic communities in the Eighteenmile Creek AOC. [ABSTRACT FROM AUTHOR]

Abstract Insensitive munitions (IMs) are replacing conventional munitions, improving safety from unintended detonation. IMs are deployed in mixture formulations but little is known about their mixture toxicology. We characterized mixture effects of the IM formulations IMX-101 (mixture of 2,4-dinitroanisole [DNAN], 3-nitro-1,2,4-triazol-5-one [NTO], and nitroguanidine [NQ]) and IMX-104 (DNAN, NTO, and hexahydro-1,3,5-trinitro-1,3,5-triazine [RDX]) in subchronic (10 d) and chronic (35 d) water-only tests in Hyalella azteca assessing impacts on survival, growth and reproduction. In 10-d single chemical exposures, DNAN was the most potent constituent, eliciting an LC50 of 16.0 mg/L; the LC50s for NTO and NQ were 891 and 565 mg/L, respectively. RDX did not elicit significant mortality up to 29.5 mg/L, a concentration near its solubility limit. Based on toxic-units (TUs), the toxicity of IMX-101 was driven by the effective concentration of DNAN; however, the presence of NTO, RDX, or both elicited interactive effects causing an approximately 2-fold decrease in lethality for IMX-104. Growth reduction was observed in 10-d exposures to DNAN, IMX-101 and IMX-104, but not for NQ, NTO, or RDX. Longer exposure duration (35 d) to IMX-101, IMX-104, and DNAN resulted in 3–6 times higher sensitivity for lethality and resulted in the most sensitive endpoint for DNAN, RDX, and IMX-101 exposures, decreased reproduction. Slight, but statistically significant, antagonistic responses among IMX-101 constituents were observed for survival and reproduction at 35d. Overall, the results support response-additive summation as a sufficient method to provide conservative hazard assessments of subchronic, chronic, and sublethal IMX-101 and IMX-104 mixture impacts in H. azteca. Highlights • Evaluated the toxicity of insensitive munitions (reduced unintended detonation). • 10 and 35d Hyalella azteca water exposures assessing survival, growth, reproduction. • Relative toxicity (10-d LC50s): DNAN > NTO > NQ; RDX not toxic near solubility limit. • Sublethal growth and reproduction effects observed for DNAN and IM formulations. • NTO, RDX or both in IM formulation caused significantly decreased toxicity of DNAN. [ABSTRACT FROM AUTHOR]

Ecotoxicological tests performed in waters with low salinities, typical of estuarine environments, are limited regarding the availability of test organisms. The amphipod Hyalella azteca, an organism protocoled for trials with freshwater sediments, presents a potential for use in saltwater tests in which the confounding factors, such as salinity and sediment grain size, should be evaluated to avoid errors in the results in relation to the sensitivity of the organism. Thus, amphipod cultivations in salinities of 0, 5, 10 and 20 were conducted, to perform tests of tolerance to salinity, and sensitivity to a reference toxicant. The tolerance of the species to different sediment grain sizes and organic matter contents was evaluated in tests with reconstituted sediments in five different compositions, varying the content of organic matter (5 to 20%), clay and sand (0 to 95%). The results of the cultivations showed that animals maintained present the best reproduction and survival rates at salinity 5, and a tolerance limit under chronic conditions, at salinity above 10. The salinity can be considered a confounding factor since the tests carried out with the reference toxicant showed the higher resistance of the species under conditions of higher salinities. The species present tolerance to different sediment grain sizes and organic matter contents; therefore, this factor does not interfere in the survival of H. azteca during the ecotoxicological tests. [ABSTRACT FROM AUTHOR]

Abstract: Uranium (U) mining and milling release arsenic (As), nickel (Ni) and U to receiving waters, which accumulate in sediments. The objective of the present study was to investigate if As, Ni, and U concentrations in tissue residue of Hyalella azteca, overlying water, sediment porewater, and solids could predict juvenile and adult survival and growth in conditions similar to lake sediments downstream of U mines and mills. We conducted 14‐d static sediment toxicity tests spiked with U, As, and Ni salts. For U, we spiked uranyl nitrate with sodium bicarbonate to limit U precipitation once in contact with circumneutral sediment. The median lethal concentrations for As, Ni, and U of juveniles and adults based on measured concentrations in sediments were 134 and 165 μg/g, 370 and 787 μg/g, and 48 and 214 μg/g, respectively. Adult survival and growth linearly decreased with increasing bioaccumulation. For juveniles, metal accumulation linearly predicted survival. We calculated median lethal body concentrations for juveniles and adults of 5 and 36 μg As/g, 14 and 49 μg Ni/g, and 0.4 and 1.0 μg U/g. The concentrations of As, Ni, and U in tissue residue leading to a 20% decrease in adult growth were 32 μg As/g, 44 μg Ni/g, and 1 μg U/g. Overall, the present study showed that U was the most toxic element, followed by As and Ni; that juveniles were more sensitive to the 3 metals tested than adults; and that threshold body concentrations can support assessment of benthic invertebrate community impairment. Environ Toxicol Chem 2018;37:2340–2349. © 2018 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals, Inc. on behalf of SETAC. [ABSTRACT FROM AUTHOR]

Global climate change (GCC) is likely to intensify the synergistic effects between altered physicochemical parameters [of changing habitats] and other anthropogenic threats, such as water pollution, posing increased risks to aquatic biodiversity. As such, it is critical to understand how organisms will respond to changes in water temperature and salinity in the presence of contaminants. We exposed the epibenthic amphipod Hyalella azteca to a 3 × 3 factorial treatment design of three temperatures and three salinities ranging from 12 to 18 °C and 0 to 8 parts per thousand (ppt), respectively, in combination with a low-level environmentally relevant concentration of the pyrethroid insecticide bifenthrin (1 ng/L). Effects on survival and swimming behavior were evaluated after 96 h exposure. Transcription of a select suite of genes was monitored at 24, 48, and 96 h using quantitative polymerase chain reaction (qPCR). Our results not only demonstrate that the changes in salinity and temperature result in negative effects to invertebrate survival, behavior, and gene response, but that the effects were significantly more pronounced in the presence of bifenthrin. This is particularly important since greater thermal fluctuations, changes in timing and extent of glacial melt, and changes in precipitation, could result in H. azteca experiencing lower temperatures at times that coincide with increased spraying of pyrethroids. These environmentally relevant exposures using the standard test species H. azteca provide essential information for understanding effects caused by GCC in conjunction with increasing pesticide use, further highlighting the need to incorporate GCC impacts into risk assessments of contaminants of concern. [ABSTRACT FROM AUTHOR]

Pesticide runoff from terrestrial environments into waterways is often lethal to freshwater organisms, but exposure may also drive evolution of pesticide resistance. We analyzed the degree of resistance and molecular genetic changes underlying resistance in Hyalella azteca, a species complex of freshwater crustaceans inadvertently exposed to pesticide pollution via runoff. We surveyed 16 waterways encompassing most major watersheds throughout California and found that land use patterns are predictive of both pyrethroid presence in aquatic sediments and pyrethroid resistance in H. azteca. Nonsynonymous amino acid substitutions in the voltage-gated sodium channel including the M918L, L925I, or L925V confer resistance in H. azteca. The most frequently identified mutation, L925I, appears to be preferred within the species complex. The L925V substitution has been associated with pyrethroid resistance in another insect, but is novel in H. azteca. We documented a variety of pyrethroid resistance mutations across several species groups within this complex, indicating that pyrethroid resistance has independently arisen in H. azteca at least six separate times. Further, the high frequency of resistance alleles indicates that pesticide-mediated selection on H. azteca populations in waterways equals or exceeds that of targeted terrestrial pests. Widespread resistance throughout California suggests current practices to mitigate off-site movement of pyrethroids are inadequate to protect aquatic life from negative ecological impacts and implies the likelihood of similar findings globally. [ABSTRACT FROM AUTHOR]

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Copyright of Ecoscience (Ecoscience) is the property of Taylor & Francis Ltd and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper deals with species sensitivity distributions (SSDs) for the lipophilic insecticide lufenuron and benthic arthropods based on sediment-spiked laboratory toxicity tests. This compound that inhibits chitin synthesis and moulting of arthropods persists in sediment. Using field-collected sediment, toxicity tests were conducted with three macro-crustaceans and six insects. The Hazardous Concentration to 5% of the tested species, the HC5 (and 95% confidence limit), derived from an SSD constructed with 10d-LC50′s was 2.2 (1.2–5.7) μg/g organic carbon (OC) in dry sediment. In addition, HC5 values derived from SSDs constructed with 28d-LC10 and 28-d LC50 values were 0.13 (0.02–1.50) μg/g OC and 2.0 (1.3–5.5) μg/g OC, respectively. In 28d toxicity tests with Chironomus riparius and Hyalella azteca, a higher sensitivity was observed when using lufenuron-spiked field-collected sediment than in lufenuron-spiked artificial sediment. Overall, the non-biting midge C. riparius appeared to be a representative and sensitive standard test species to assess effects of lufenuron exposure in sediment. The Tier-1 (based on standard test species), Tier-2 (based on standard and additional test species) and Tier-3 (model ecosystem approach) regulatory acceptable concentrations (RACs) for sediment-spiked lufenuron did not differ substantially. The Tier-2 RAC was the lowest. Since to our knowledge this study is the first in the open literature that evaluates the tiered approach in the sediment effect assessment procedure for pesticides, we advocate that similar evaluations should be conducted for pesticides that differ in toxic mode-of-action. [ABSTRACT FROM AUTHOR]

Pyrethroid-resistant Hyalella azteca with voltage-gated sodium channel mutations have been identified at multiple locations throughout California. In December 2013, H. azteca were collected from Mosher Slough in Stockton, CA, USA, a site with reported pyrethroid (primarily bifenthrin and cyfluthrin) sediment concentrations approximately twice the 10-d LC50 for laboratory-cultured H. azteca. These H. azteca were shipped to Southern Illinois University Carbondale and have been maintained in pyrethroid-free culture since collection. Even after 22 months in culture, resistant animals had approximately 53 times higher tolerance to permethrin than non-resistant laboratory-cultured H. azteca . Resistant animals held in culture also lacked the wild-type allele at the L925 locus, and had non-synonymous substitutions that resulted in either a leucine-isoleucine or leucine-valine substitution. Additionally, animals collected from the same site nearly three years later were again resistant to the pyrethroid permethrin. When resistant animals were compared to non-resistant animals, they showed lower reproductive capacity, lower upper thermal tolerance, and the data suggested greater sensitivity to, 4, 4′-dichlorodiphenyltrichloroethane (DDT), copper (II) sulfate, and sodium chloride. Further testing of the greater heat and sodium chloride sensitivity of the resistant animals showed these effects to be unrelated to clade association. Fitness costs associated with resistance to pyrethroids are well documented in pest species (including mosquitoes, peach-potato aphids, and codling moths) and we believe that H. azteca collected from Mosher Slough also have fitness costs associated with the developed resistance. [ABSTRACT FROM AUTHOR]

In the frame of a project which consists in modeling a laboratory microcosm under cadmium pressure, we initiated this study on the fate and effects of cadmium in the presence of either the microalga Pseudokirchneriella subcapitata or the duckweed Lemna minor, two organisms of the microcosm. For each organism, growth inhibition tests on a duration of 2–3 weeks were carried out with the objective of linking effects with total dissolved, ionic and internalized forms of cadmium. Numbers of organisms (algal cells or duckweed fronds) in 2-L beakers filled with synthetic nutritive medium containing EDTA were counted during the course of assays, while cadmium concentrations in the water and in the organisms were measured. Free cadmium fraction was calculated using PHREEQC, a computer program for chemical speciation. Results showed that cadmium toxicity to microalgae could be correlated to the free divalent fraction of this metal, limited by the presence of EDTA, and to its concentration in the organisms. Bioconcentration factors for our medium were suggested for P. subcapitata (111,000 on the basis of free cadmium concentration) and L. minor (17,812 on the basis of total dissolved concentration). No effect concentrations were roughly estimated around 400 µg/g for Pseudokirchneriella subcapitata and 200–300 µg/g for Lemna minor. This study is a first step towards a fate model based on chemical speciation for a better understanding of microcosm results. [ABSTRACT FROM AUTHOR]

Abstract: Pyrethroid insecticides are commonly used in pest control and are present at toxic concentrations in surface waters of agricultural and urban areas worldwide. Monitoring is challenging as a result of their high hydrophobicity and low toxicity thresholds, which often fall below the analytical methods detection limits (MDLs). Standard daphnid bioassays used in surface water monitoring are not sensitive enough to protect more susceptible invertebrate species such as the amphipod Hyalella azteca and chemical loss during toxicity testing is of concern. In the present study, we quantified toxicity loss during storage and testing, using both natural and synthetic water, and presented a tool to enhance toxic signal strength for improved sensitivity of H. azteca toxicity tests. The average half‐life during storage in low‐density polyethylene (LDPE) cubitainers (Fisher Scientific) at 4 °C of 5 pyrethroids (permethrin, bifenthrin, lambda‐cyhalothrin, cyfluthrin, and esfenvalerate) and one organophosphate (chlorpyrifos; used as reference) was 1.4 d, and piperonyl butoxide (PBO) proved an effective tool to potentiate toxicity. We conclude that toxicity tests on ambient water samples containing these hydrophobic insecticides are likely to underestimate toxicity present in the field, and mimic short pulse rather than continuous exposures. Where these chemicals are of concern, the addition of PBO during testing can yield valuable information on their presence or absence. Environ Toxicol Chem 2018;37:462–472. © 2017 SETAC [ABSTRACT FROM AUTHOR]

The US Environmental Protection Agency (USEPA) is reviewing the protectiveness of the national ambient water quality criteria (WQC) for aluminum (Al) and compiling a toxicity data set to update the WQC. Freshwater mussels are one of the most imperiled groups of animals in the world, but little is known about their sensitivity to Al. The objective of the present study was to evaluate acute 96-h and chronic 28-d toxicity of Al to a unionid mussel ( Lampsilis siliquoidea) and a commonly tested amphipod ( Hyalella azteca) at a pH of 6 and water hardness of 100 mg/L as CaCO3. The acute 50% effect concentration (EC50) for survival of both species was >6200 μg total Al/L. The EC50 was greater than all acute values in the USEPA acute Al data set for freshwater species at a pH range of 5.0 to <6.5 and hardness normalized to 100 mg/L, indicating that the mussel and amphipod were insensitive to Al in acute exposures. The chronic 20% effect concentration (EC20) based on dry weight was 163 μg total Al/L for the mussel and 409 μg total Al/L for the amphipod. Addition of the EC20s to the USEPA chronic Al data set for pH 5.0 to <6.5 would rank the mussel ( L. siliquoidea) as the fourth most sensitive species and the amphipod ( H. azteca) as the fifth most sensitive species, indicating the 2 species were sensitive to Al in chronic exposures. The USEPA-proposed acute and chronic WQC for Al would adequately protect the mussel and amphipod tested; however, inclusion of the chronic data from the present study and recalculation of the chronic criterion would likely lower the proposed chronic criterion. Environ Toxicol Chem 2018;37:61-69. Published 2017 Wiley Periodicals Inc. on behalf of SETAC. This article is a US government work and, as such, is in the public domain in the United States of America. [ABSTRACT FROM AUTHOR]